Hackers took only a few weeks to unlock the new AppleTV’s operating system. Apple wants you to use the $100 aTV2 to watch video from your computer on your TV and to buy movies exclusively from iTunes. But with the “jailbreak,” you can stream video from any app, not just iTunes, and add homegrown software to get extras like a Web browser and a weather interface. Look for many more tweaks this year as well. Here’s how to unlock your aTV2, plus a few other tricks.